Despite
their small size...all thunderstorms are dangerous. Every
thunderstorm produces lightning...which kills more people
each year than tornadoes.
-
Occurs
with all thunderstorms
-
Averages
93 deaths and 300 injuries nationwide each year
-
Causes
several hundred million dollars in property damage and
forests each year.
|
Photo by Phoenix Gazette
|
|
|
Heavy rains
from thunderstorms can lead to flash flooding.
|
Photo by David Vann, The Sentinel-Record
Hot Springs AR
|
|
Damaging straight-line winds are another threat posed
by thunderstorms...
- Responsible for most thunderstorm wind
damage
- Winds can exceed 100 miles per hour!
|
Photo by: Dr. T. Theodore Fujita
Hundreds of trees were blown down by straight-line winds in
Sawyer County Wisconsin in July 1977
One type of straight-line
wind ... the downburst or microburst ... can cause damage equivalent to a strong tornado and can be extremely dangerous to aviation. |
|
Hail is another costly threat posed by thunderstorms
- Causes nearly $1 billion in damage to property and crops each year
- According to NOAA, the Kansas City hail storm on April 10, 2001 was the costliest hail storm in the U.S. which caused damages of an estimated $2 billion.
|
Photo from
National Center for Atmospheric Research
|
|
|
Tornadoes are nature's most violent storms
|
Photo by Greg Stumpf
|
|
How do thunderstorms develop?
Every thunderstorm needs three ingredients:
- Moisture - to form clouds and rain
- Unstable air - relatively warm air that can rise
rapidly
- Lift - fronts, sea breezes, and mountains are
capable of lifting air to form thunderstorms.
|
Winds bring moisture from the ocean over the land
area...lift is provided by approaching cooler, drier, more
dense air (a cold front)
|
|
In the developing stage...rising warm air carries moisture
aloft into cooler air where the moisture condenses and builds the clouds vertically.
- Towering cumulus clouds indicate rising air
- Usually little if any rain during this stage
- Lasts about 10 minutes
- Occasional lightning during this stage
|
 |
|
In the mature stage...
- Most likely time for hail, heavy rain, frequent
lightning, strong winds and tornadoes
- Storm occasionally has a black or dark green
appearance
- Lasts an average of 10 to 20 minutes but may last
much longer in some storms
|
 |
|
|
In the dissipating stage...rain cooled air flowing out of the
thunderstorms cuts of the supply of warm unstable rising air
-
Rainfall decreases in intensity
-
Some thunderstorms produce a burst of strong
winds during this stage
-
Lightning remains a danger during this stage
|
 |
|
Where are thunderstorms most likely? Across
much of Georgia and in central and southern South Carolina there are an average of 50 to 70 days with thunderstorms each year. From the Pee Dee
region to the Upstate of South Carolina there are an average of 30 to 50 days each year with
thunderstorms.
Thunderstorms are most likely to happen in the spring and summer
and during the afternoon and evening hours - but in South Carolina and Georgia
thunderstorms can develop year-round and at all
hours. |
Thunderstorms are common during the
spring and summer across the southeastern U.S. |
|
The National Weather Service considers a thunderstorm severe only if it produces
...
|
Damaging Wind Gusts
58 miles per hour (50
knots) or higher
or |
Large Hail
3/4 inch in diameter
(penny size) or larger
or |
Tornadoes |
Of the estimated 100,000 thunderstorms that occur each year in the United States,
only 10 percent (or 10,000) are classified as severe. |
|
The National Weather Service issues watches and warnings for severe thunderstorms
A SEVERE THUNDERSTORM WATCH means
conditions are favorable for thunderstorms to
become severe...or severe thunderstorms to move into the watch area. Watches are
intended to heighten public awareness of the possible severe
weather threat. Keep an eye on the sky and stay tuned to NOAA Weather Radio or local radio,
television, or cable to know when severe weather warnings are issued for your area.
A SEVERE THUNDERSTORM WARNING means
a severe thunderstorms poses an imminent danger to life and property to those in the path of the
storm. When severe weather is indicated by weather radar, or is reported by trained
SKYWARN Severe Weather Spotters or law enforcement
officials a warning is issued immediately.
|
Severe Thunderstorm warnings are sent to local radio and
television stations and are broadcast over your local NOAA Weather Radio serving the warning area. These
warnings are also relayed to local emergency management and public safety officials who can activate
local warning systems to alert communities to the danger.
|
|
Contact us if you'd like a free copy of
Thunderstorms...Tornadoes...Lightning...Nature's Most Violent
Storms - a preparedness brochure produced by the National Weather Service, Federal Emergency Management Agency, and the American Red Cross.
Related Web Sites on Lightning and Lightning Safety:
|
weather.gov 
